The present invention generally relates to inkjet and other types of printers and more particularly, to a printing system with thermally efficient heat transfer capabilities for a printhead portion of an inkjet printer.
Inkjet printers are commonplace in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes a printing medium, such as paper.
An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes xe2x80x9cdot locationsxe2x80x9d, xe2x80x9cdot positionsxe2x80x9d, or pixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
In general, the small drops of ink are ejected from the nozzles through orifices by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and be ejected from the orifices. Specifically, for one dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated for superheating a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and, consequently, a droplet of ink is ejected from the nozzle and onto a print media. One very important factor in assuring high print quality is the accuracy of the trajectory of the ejected droplet since this affects where it lands upon the print media. The accuracy of this trajectory is mostly dependent upon the particular geometry of the nozzle.
One challenge in controlling the nozzle geometry and hence trajectory of the droplets is to regulate bending and/or buckling of the nozzle member, otherwise known as xe2x80x9cdimplingxe2x80x9d of the nozzle member. Dimpling of the nozzle member causes the nozzles to be skewed, which leads to imprecise nozzle geometry. Dimpling tends to be induced during print cartridge manufacturing, which includes cartridge assembly processes such as adhesively bonding the printhead to the cartridge. More specifically, dimpling can be caused by inadvertent bending and/or buckling of the nozzle member due to structural thermal expansions and contractions occurring when the nozzle member is adhesively sealed to the print cartridge. For example, during the heat, cure and cool process when the nozzle member is adhered to the cartridge, the cartridge experiences thermal expansions and contractions. These thermal expansions and contractions cause the nozzle member to buckle, bend and deform, thereby skewing the nozzles. Typical heat and cure processes include curing the adhesive by applying hot air to the nozzle member, which heats an upper portion of the print cartridge.
Since dimpling of the nozzle member skews the nozzles, it tends to adversely affect nozzle geometry, thereby causing nozzle trajectory errors. A measure of this bending of the nozzle member is referred to as the xe2x80x9cnozzle camber anglexe2x80x9d (NCA), which is proportional to the bending of the nozzle member from an ideal flat state. Poor nozzle camber angles (NCAs) causes ink drop trajectory errors and uncontrolled ink drop directionality. In other words, when the printhead assembly is scanned across a recording medium, the NCA-induced ink drop trajectory errors will affect the location of printed dots and, thus, affect the quality of printing. Also, the bending of the nozzle member can restrict ink flow into nozzles, thus limiting the refill speed and hence the maximum droplet ejection frequency. This is turn limits printer speed. Therefore, what is needed is a nozzle member that has incurred limited bending or deformation during manufacturing of the print cartridge and to be as flat as possible. What is also needed is a printing system incorporating a device that reduces dimpling of a nozzle member during manufacture of a printhead portion of an inkjet printer.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a printing system with thermally efficient heat transfer capabilities for reducing dimpling of a nozzle member during fabrication of the printhead portion of an inkjet printer.
The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body having a heat transfer device, ink channels and a nozzle member having plural nozzles coupled to respective ink channels. The nozzle member is secured to the printhead body with a suitable adhesive layer. The heat transfer device can be defined by a portion of or the entire printhead body for reducing thermal expansion of the printhead body during exposure to heat. Namely, the heat transfer device of the printing system of the present invention is capable of efficiently reducing thermal expansion (which in turn reduces the thermal contraction) of the printhead body during the process of adhering (which includes heating and curing the adhesive) the nozzle member to the printhead body. As a result, trajectory errors of ejected ink droplets from the nozzles are reduced.
In another embodiment, a controlled process is used to heat and cure the adhesive for reducing the amount of heat applied to the printhead body, thereby reducing the thermal expansion of the printhead body. In particular, hot gimbaled rails can be placed in direct contact with the nozzle member to conductively heat and cure the adhesive directly below the contact area between the nozzle member and printhead body. Since the rails only contact the nozzle member, heat can be applied to localized areas with controlled amounts. For instance, a minimum required amount of heat to cure the adhesive can be applied to a controlled area directly above the adhesive. As a result, only a portion of the printhead body is heated, thereby efficiently reducing thermal expansion of the printhead body. Consequently, trajectory errors of ejected ink droplets from the nozzles are reduced.